Many commercially important consumer devices require management of light into a space. Examples include various displays such as televisions, computer displays, projection screens, illuminated signs, and light fixtures (luminaires). In each of these applications, there may be an optimum “far-field” pattern of light for achieving the best combination of performance and efficiency. The “far-field” pattern, broadly speaking, describes the variation of brightness of light transmitted from a source and illuminating a distant surface. For example, the far-field pattern of a flashlight may be visualized by shining the light on to a dark wall at some distance from the flashlight, and observing the variation in brightness on the wall.
In ceiling-mounted light fixtures, lighting designers generally strive to provide a far-field illumination pattern that fills a desired space with an even illumination pattern. For ceiling-mounted light fixtures, light exiting the luminaire in a downward direction (perpendicular to the ceiling and floor) provides far-field illumination that is most favorable for achieving usable lighting, while light that exits in a sideward direction (parallel to the ceiling and floor) tends to illuminate wall areas, which may indirectly contribute to a desirable illumination pattern. Light exiting the fixture at intermediate angles, most particularly at angles between 60-85° from vertical, are least desirable, since this light contributes little to illumination in the vicinity of the fixture, and also contributes to “glare zone” light that may be annoying or distracting to occupants in the illuminated space. Light exiting in the glare zone angles of 60-85°may be too easily seen by occupants at relatively short distances from the light. This light may be much brighter than the surrounding illumination because it is observed directly rather than as diffuse reflection from objects in the illuminated space. This glare light may reflect from work surfaces and video displays, reducing visibility.
For decades, lighting manufacturers have devised various approaches for minimizing glare light from ceiling fixtures. Approaches include mechanically baffling the fixture so light rays that would otherwise exit the fixture in the “glare zone” instead strike an opaque barrier that either reflects or absorbs the light. Other approaches use parabolically or ellipsoidally shaped reflectors to reflectively direct most light in a downward direction, thereby reducing light exiting in the glare zone. Yet another approach is the use of one or more refractive lenses or arrays of refractive lenses that help to direct light in a more downward direction, away from the glare zone. These approaches have been used alone or in combination. Some approaches are embodied in U.S. Pat. Nos. 4,703,405; 4,725,934; 4,907,143; 4,947,303; 5,363,293; 5,486,989; 5,730,521; 6,027,231; 6,193,394; 6,354,725; 6,698,908; 7,156,540; 7,213,948; 7,660,039; and 7,837,361.
Although glare control approaches described above may be effective in controlling glare in luminaires with conventional light sources such as fluorescent lamps, these approaches generally are not effective in “lamp hiding” i.e. obscuring the source of illumination when viewed directly. This lack of hiding ability has been accepted in the industry because the lamp image produced by conventional sources is not considered an aesthetic liability by most lighting designers. Structures used in most glare control approaches share the characteristic of being easily visible to a viewer, for example, an array of louvers arranged in a grid pattern to reduce glare in a fluorescent ceiling troffer. Use of visible structures for glare control generally prevents the lighting designer from achieving a “smooth” look, whereby the output face of the light provides a clean, uniform glow. Moreover, glare control achieved by mechanical structures may be less efficient since glare light may be absorbed rather than redirected toward non-glare exit angles.
Certain conventional glare-control sheets are made using a transparent sheet with cone-shaped protrusions on one surface and a smooth opposing surface. When applied to a light with the smooth surface facing the light source and the cone surface facing the viewer, such glare-control sheets can use refraction to effectively limit the light at high angles, as described, for example, in U.S. Pat. No. 2,474,317. These conventional refractive glare control products often use arrays of cones of substantially identical base angle, and often using a base diameter of one to several millimeters. They often have a harsh “cutoff” in which the intensity drops rapidly at the edge of the “glare zone” and creates unwanted visual effects. These can include to the perception of a dark zone crossing the surface of the luminaire, and in some cases color separation (such as orange edges) at the edge of the dark zone.
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to claims in this application and any application claiming priority from this application, are not admitted to be prior art by inclusion of this section, and may be attributed to the present inventors' appreciation of the problem to be solved.